The present invention generally relates to a wafer cassette/loadport assembly used on a microelectronic fabrication equipment and a method of using and more particularly, relates to a wafer cassette/loadport assembly with a built-in self-identification function and a method for operating the assembly.
The conveying of a semiconductor wafer is important in the manufacturing of integrated circuit chips due to the delicate nature of the wafer. In fabricating an IC product, a multiplicity of fabrication steps, i.e. as many as several hundred, is required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor 7 deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
In modern semiconductor fabrication facilities, especially for the 200 mm or 300 mm fabrication plants, automatic guided vehicles (AGV) and overhead hoist transport (OHT) are extensively used to automate the wafer transport process as much as possible. The AGV and OHT utilize the input/output ports of a stocker to load or unload wafer lots, i.e. normally stored in FOUFs. FIG. 1 is a perspective view of an overhead hoist transport system 32 consisting of two vehicles 34, 36 that travel on a track 38. An input port 40 and an output port 42 are provided on a stocker 30. As shown in FIG. 1, the overhead transport vehicle 36 stops at a position for unloading a FOUP 44 into the input port 40. The second overhead transport vehicle 34 waits on track 38 for input from stocker 30 until the first overhead transport vehicle 36 moves out of the way.
Similarly, the OHT system is used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 2. A cassette pod 10 of the FOUP type is positioned on a loadport 12 of a process machine 14. The loadport 12 is equipped with a plurality of locating pins 16 for the proper positioning of the cassette pod 10. A detailed perspective view of the FOUP 10 is shown in FIG. 3. The FOUP 10 is constructed by a body portion 18 and a cover portion 28. The body portion 18 is provided with a cavity 46 equipped with a multiplicity of partitions 48 for the positioning of 25 wafers of the 300 mm size. The body portion 18 is further provided with sloped handles 50 on both sides of the body for ease of transporting. On top of the body portion 18, is provided with a plate member 52 for gripping by a transport arm (not shown) of the OHT system (not shown).
When a wafer cassette is loaded onto a loadport of a process machine, problems occur when the cassette is not correctly identified leading to serious cross-contamination problems for the wafers contained in the cassette. For instance, in the same intra-bay, there may be twenty or thirty process machines each used for depositing a different material layer, for instance, the chemical vapor deposition of silicon oxide, polysilicon, copper or cobalt. When a wafer cassette, such as a FOUP is positioned on the wrong process machine that is setup for the deposition of a different material, the resulting contamination on wafers can be detrimental and extremely difficult to correct.
It is therefore an object of the present invention to provide a wafer cassette/loadport assembly that does not have the drawbacks or shortcomings of the conventional wafer cassette/loadport assemblies.
It is another object of the present invention to provide a wafer cassette/loadport assembly that is equipped with a built-in self-identification system.
It is a further object of the present invention to provide a wafer cassette/loadport assembly that is capable of self-identifying the type of wafer cassette placed on the loadport of a process machine.
It is another further object of the present invention to provide a wafer cassette/loadport assembly that has built-in, self-identification system for feeding information on the wafer cassette into a process controller.
It is still another object of the present invention to provide a wafer cassette/loadport assembly that has a built-in, self-identification system by providing conductive pins on the loadport as locating pins.
It is yet another object of the present invention to provide a method for identifying a wafer cassette that is positioned on a loadport by utilizing a built-in, self-identification system.
It is still another further object of the present invention to provide a method for identifying a wafer cassette positioned on a loadport by feeding information on the wafer cassette into a process controller and comparing to data stored therein.
In accordance with the present invention, an apparatus and a method for identifying a wafer cassette by a built-in, self-identification system are provided.
In a preferred embodiment, a wafer cassette/loadport assembly that has a built-in, self-identification system is provided which includes a wafer cassette equipped with a bottom plate having at least two recessed holes in a bottom surface of the plate, at least one of the at least two recessed holes is provided with a spring-loaded, laterally positioned, electrically conductive plate adapted to engage one of at least two pins situated on a top surface of a loadport; a loadport equipped with at least two pins on a top surface in positions that are in mirror image to the two recessed holes in the wafer cassette when the wafer cassette is placed on top of the loadport, each of the at least two pins is provided with two electrically conductive tips that are spaced-apart and electrically insulated from each other, the two tips are adapted to conduct electricity therein between when pressed against and intimately contact the spring-loaded, electrically conductive plate in one of the at least two recessed holes upon engagement between the loadport and the wafer cassette thereby sending an electrical signal to a process controller identifying the wafer cassette.
The wafer cassette/loadport assembly that has built-in, self-identification system may further include a process controller for receiving the electrical signal from the loadport and comparing to pre-stored data in the process controller. A number of the at least two recessed holes on the wafer cassette equals a number of the at least two pins on top of the loadport. The at least two pins on a top surface of the loadport are locating pins. The two electrically conductive tips are formed of aluminum, stainless steel or copper. The two electrically conductive tips are each connected by a lead wire for sending signals to the process controller, and each formed in a cylindrical-shaped rod, or each formed in a half-circular columnar shape. The two electrically conductive tips are each supported by a common base formed of an electrically insulating material, such as a ceramic or a non-conductive plastic. The wafer cassette may have two recessed holes and both recessed holes are equipped with the spring-loaded, laterally positioned, electrically conductive plate. The wafer cassette may further have two recessed holes wherein only one of the two holes is equipped with the spring-loaded, laterally positioned, electrically conductive plate.
The present invention is further directed to a method for identifying a wafer cassette positioned on a loadport which can be carried out by the operating steps of providing a wafer cassette that is equipped with a bottom plate that has at least two recessed holes in a bottom surface of the plate, at least one of the at least two recessed holes is provided with a spring-loaded, laterally positioned, electrically conductive plate adapted to engage one of the at least two pins situated on a top surface of a loadport; providing a loadport equipped with at least two pins on a top surface in positions that are in mirror image to the two recessed holes in the wafer cassette when the wafer cassette is placed on top of the loadport, each of the at least two pins is provided with two electrically conductive tips that are spaced-apart and electrically insulated from each other, the two tips are adapted to conduct electricity therein between when pressed against and intimately contact the spring-loaded, electrically conductive plate in one of the at least two recessed holes upon engagement between the loadport and the wafer cassette; and sending an electrical signal from the loadport to a process controller identifying the wafer cassette.
The method for identifying a wafer cassette positioned on a loadport may further include the step of providing two recessed holes each equipped with a spring-loaded, laterally positioned, electrically conductive plate. The method may further include the step of providing two recessed holes wherein only one is equipped with a spring-loaded, laterally positioned, electrically conductive plate. The method may further include the step of forming the two electrically conductive tips in aluminum, stainless steel or copper. The method may further include the step of forming the two electrically conductive tips in a cylindrical-shaped rod, or in half-circular columnar shape. The method may further include the step of forming the two electrically conductive tips on a common base formed of an electrically insulating material, such as a ceramic or a non-conductive plastic.